Typically, it is known that, in optical transport network systems, Wavelength Division Multiplexing (WDM) is implemented so as to multiplex optical signals having a plurality of different wavelengths and transmit the multiplexed signal through a single optical fiber. In such an optical transport network system, a plurality of optical transmission devices is installed for transmitting wavelength-multiplexed optical signals.
In an optical transport network system, at the time of setting transmission paths via which optical signals are to be transmitted between optical transmission devices; the transmission paths are selected by calculating whether or not the optical parameters requested by the optical transport network system are satisfied, so as to ensure what is called reachability of optical signals. For that reason, in an optical transport network system, every time a routing request is issued; complex processes related to the network design, such as determining whether or not the optical parameters are satisfied, are performed. Meanwhile, the optical parameters point to, for example, the effect on signals by optical loss/chromatic dispersion/PMD (Polarization Mode Dispersion).    Patent Literature 1: International Publication Pamphlet No. WO 2005/032076
However, in a typical optical transport network system; the mechanism of an optical transmission device autonomously selecting a transmission path for optical signal transmission is not taken into consideration.
That is, in a typical optical transport network system, since calculating the reachability of optical signals requests a heavy processing load, the reachability calculation is performed using an Off-Line tool that is installed in an element manager which manages a plurality of optical transmission devices. Thus, in a typical optical transport network system, every time a routing request is issued; the transmission path for optical signal transmission is selected using the Off-Line tool, and the selection result is set in the optical transmission devices. Therefore, there are times when the operation of selecting the transmission path for optical signal transmission is complex.